Soon-Yi Previn was born in South Korea. Previn's true age and date of birth are unknown, but are estimated based on a bone scan;[1] her passport indicates a date of birth of October 8, 1970.[2] According to Vanity Fair, Previn's biological mother was a prostitute who would slam a door on Soon-Yi's head as a form of punishment.[1] Abandoned as a young child, Previn wandered around the streets of Seoul starving and living out of trash cans.[3] In 1978, Previn was adopted by Mia Farrow and André Previn and relocated to the United States;[4] at the time, she spoke no known language and reportedly battled learning disabilities.[1][4] Rose Styron acts as her godmother.[1]

In 1979, Mia Farrow ended her marriage to Andre Previn and began a long-term relationship with Woody Allen.[5] Allen later adopted two of Farrow's adopted children: Dylan Farrow (also known as Eliza) and Moses Farrow. The couple gave birth to Ronan Farrow, also known as Satchel.

During her teens, Previn made an uncredited appearance in Hannah and Her Sisters (1986), which starred her adopted mother Mia Farrow and was directed by her future husband Woody Allen. Previn appeared as an extra in Allen's 1991 film entitled Scenes from a Mall.[1] Previn also appeared alongside Allen in the documentary Wild Man Blues (1997).[9]

Previn's intimate relationship with Woody Allen began in the late 1980s during Allen's relationship with Previn's adoptive mother, Mia Farrow.[10] Allen described his relationship with Previn as a "fling" that developed into a more significant relationship.[10] He has also both affirmed and denied that he acted as a paternal figure to Previn.[11] Their affair came to light when Farrow allegedly discovered Allen's pornographic Polaroid photographs of Previn in late 1991 or early 1992.[1][4][12] While Previn denies sexual assault on Allen's part, there are accounts suggesting that she was not the author of her published statements on the subject.[1][8] Previn's relationship with Allen became public and "erupted into tabloid headlines and late-night monologues in August 1992."[13] Farrow broke off her relationship with Allen in 1992 following the discovery of Allen's affair with Previn.[14] As of 2006, Previn remained estranged from Farrow.[15]